1. Field of the Invention
The present invention relates to a high-frequency module including a plurality of filter elements.
2. Description of the Related Art
A portable device or the like with a wireless communication function includes a filter circuit in order to allow passage of only a high-frequency signal of a desired frequency, and to attenuate a high-frequency signal having a frequency other than the desired frequency.
For example, Japanese Unexamined Patent Application Publication No. 2012-109818 discloses a filter circuit including a plurality of SAW (surface acoustic wave) filters. More specifically, the filter circuit of Japanese Unexamined Patent Application Publication No. 2012-109818 includes the plurality of SAW filters connected in series between an input terminal and an output terminal. A SAW filter is further connected between a connection line, which interconnects an adjacent pair of the SAW filters connected in series, and a ground.
In the filter circuit disclosed in Japanese Unexamined Patent Application Publication No. 2012-109818, an inductor or a series circuit of an inductor and a capacitor (called a compensation circuit) is connected in parallel to the series circuit of the SAW filters for the purpose of improving attenuation characteristics outside a passband. On that occasion, the compensation circuit is adjusted such that a high-frequency signal (one suppression target signal) being outside the passband and propagating through a circuit section, which is defined by a group of SAW filters, and the other suppression target signal propagating through the compensation circuit have amplitudes that match with each other and phases that are reversed to each other. As a result, both the suppression target signals are canceled out at a connection point between the circuit section defined by the group of SAW filters and the compensation circuit, and are not output from an output terminal.
In the above-described structure, however, the compensation circuit, i.e., the inductor or the series circuit of the inductor and the capacitor, has to be disposed in addition to the circuit section, which is defined by the group of SAW filters and which has the main filter function, for the purpose of just improving the attenuation characteristics.
Accordingly, the number of constituent elements of the filter circuit increases, and the size of the filter circuit increases. Thus, the above-described related art is not suitable for currently-used portable terminals, etc., which are demanded to have smaller sizes.